In recent years, for the hermetic-type compressor provided in the refrigerating cycle, to reduce the noise in the operation and to reduce the power consumption have strongly been desired on the assumption that the hermetic-type compressor should have high reliability. In order to meet such demand, some progresses have been made to lower rotational frequency of the compressor by driving it with an inverter and to lower viscosity for the lubricant oil to be used. In the case of performing a low-speed operation of such compressor using lubricant oil having low viscosity, it is an important task to supply the lubricant oil certainly to the sliding portions in the compressor. Namely, as such task for the recent hermetic-type compressors, it is an improvement in the reliability of the sliding portions by certainly supplying lubricant oil. In order to achieve the task, an oil pump for supplying lubricant oil to the sliding portions has been already improved in some conventional hermetic-type compressor. As such conventional hermetic-type compressor, there is one example disclosed in the Official Gazettes of Japanese Unexamined Patent Publication No. 2000-110723.
In the following paragraphs, the conventional hermetic-type compressor disclosed in the Official Gazettes of Japanese Unexamined Patent Publication No. 2000-11023 will be explained with reference to FIG. 6 of the appended drawings.
FIG. 6 is a longitudinal cross-sectional view illustrating an inner structure of the conventional hermetic-type compressor. As shown in FIG. 6, an electric motor part 4 composed of a stator 2 and a rotor 3, and a compressor part 5 to be driven by the electric motor part 4 are contained in a hermetically sealed container 1. In the hermetically sealed container 1, a lubricant oil 6 is reserved.
A crank shaft 7, which serves to transmit the rotational driving force of the electric motor part 4 to the compressor part 5, has a main shaft 8 to which the rotor 3 is press-fit to be fixed and a crank part 9 formed on the main shaft 8. The crank part 9 is formed eccentrically with respect to the rotational center axis of the main shaft 8. A cylinder block 14 in the compressor part 5 includes a compressing chamber 15 having approximately cylindrical shape as well as a main shaft bearing 16 which rotatably supports the main shaft 8. On the outer periphery of the main shaft 8, there are provided two sliding sections 17, 17, being in a sliding engagement with the main shaft bearing 16 at its upper and lower parts, and a non-sliding section 18 which does not contact to slide with the main shaft bearing 16, and which is formed between the sliding parts 17,17.
In the compressor part 5, a piston 19 is inserted in the compressing chamber 15 of the cylinder block 14, being permitted of a reciprocating sliding movement in the chamber. The piston 19 is connected to the crank part 9 of the crank shaft 7 with a connecting rod 20.
In the crank shaft 7, an oil supplying path 30 is formed inside the main shaft 8 and another oil supplying path 31 is formed from the upper potion of the main shaft 8 to the crank part 9. On the outer periphery of the main shaft 8, there is formed a spiral groove 32 which inclines upwards in a direction reverse to the rotational direction of the crank shaft 7. An lower end of the spiral groove 32 communicates with the oil supplying path 30 at the vicinity of its upper end. An upper end of the spiral groove 32 communicates with the other oil supplying path 31 at the vicinity of its lower end. On the lower end of the main shaft 8, there is fixed an oil pump 33 whose one end opens in the lubricant oil 6 and whose another end communicates with the oil supplying path 30.
Next, the operation of the above-mentioned conventional hermetic-type compressor will be hereinafter described.
The crank shaft 7 rotates with the rotational movement of the rotor 3 of the electric motor part 4, and its crank part 9 performs a revolving movement about the center axis of the main shaft 8. The revolving movement of the crank part 9 is converted into a reciprocating movement with the connecting rod 20 to be transmitted to the piston 19. As a result, the piston 19 performs a reciprocating sliding movement within the compressing chamber 15, thereby to suck a refrigerant gas into the compressing chamber 15 to be compressed. In this manner, the refrigerant gas in the refrigerating system is, after being sucked into the compressing chamber 15 to be compressed therein, is then exhausted outside the hermetically sealed container for a further circulation through the refrigerating system.
The oil pump 33 provided on the lower end of the crank shaft 7 performs a pumping action of pumping up the lubricant oil 6 by the rotation of the crank shaft 7. By the pumping action of the oil pump 33, the lubricant oil 6 reserved in the bottom portion of the hermetically sealed container 1 ascends through the oil supplying path 30 in the main shaft 8. The lubricant oil 6 reached the upper portion of the oil supplying path 30 is led to the spiral groove 32. Since the spiral groove 32 inclines in the same direction of an inertia force which acts in a direction reverse to the rotational direction of the crank shaft 7, an upward transporting force acts on the lubricant oil 6 in the groove 32. As a result, the lubricant oil 6 ascends along the groove 32 and is supplied to the sliding section 17 of the crank shaft 7. And the lubricant oil 6 reached the upper end of the spiral groove 32 is led to the other oil supplying path 31 to be supplied to the sliding components of the crank part 9 and the compressor part 5.
In the conventional hermetic-type compressor structured in the above-mentioned manner, there is the case wherein minute dust and refuses generated during the assembling process may enter the lubricant oil 6. The minute dust and refuses sucked up with the lubricant oil 6 by the oil pump 33 ascend through the oil supplying path 30 by centrifugal force. Since the oil supplying path 30 is formed in the main shaft 8 along a perpendicular line which is eccentric with respect to the center line of the main shaft 8, the minute dust and the like ascend through the oil supplying path 30 along its outer peripheral side. And the minute dust and the like are thrown away at the vicinity of the oil supplying path 30 towards the direction of the spiral groove 32 formed on the outer periphery of the main shaft 8 by centrifugal force. Namely, the direction of the stream of the lubricant oil 6 changes by approximately 90 degrees to the horizontal direction at the vicinity of the oil supplying path 30. For that reason, the minute dust and the like are easily collected around the vicinity of the lower end of the spiral groove 32 by centrifugal force and gravity. When the minute dust and the like are collected around the vicinity of the lower end of the groove 32, the minute dust and the like easily enter into the narrow gap between the sliding sections 17 of the crank shaft 7 and the main shaft bearing 16, which is a factor of hindering the smooth sliding movement. As a result, the input energy must be increased to obtain the desired output in the conventional hermetic-type compressor, thus inviting a decrease in the efficiency. In addition, there is a problem that the reliability lowers due to the damage at the sliding sections 17.
Moreover, in the case where the conventional hermetic-type compressor is driven by the inverter at a low-speed driving frequency not greater than that of the power source, when the minute dust and the like are thrown away at the vicinity of the lower end of the groove 32 towards its periphery by centrifugal force, they further tend to stagnate at the lower end of the groove 32 by gravity because the flow velocity of the lubricant oil 6 is slow. Therefore, in the case of driving the conventional hermetic-type compressor at a low speed, the minute dust and small refuses further easily enter into a narrow gap between the sliding sections 17 and the main shaft bearing 16, thus damaging the smooth sliding movement.
The present invention is proposed to solve the above-mentioned problems of the conventional hermetic-type compressor and intends to provide a hermetic-type compressor having a high efficiency and reliability. In the present invention, the expected smooth sliding movement is realized by structuring the compressor so that the lubricant oil can sufficiently be supplied to the sliding parts and components, and preventing the dust and the refuses from entering the sliding parts and components in the shaft portion.